We have used the newly engineered transposable element Dsg to tag a gene that gives rise to a defective kernel (dek) phenotype. Dsg requires the autonomous element Ac for transposition. Upon excision, it leaves a short DNA footprint that can create in-frame and frameshift insertions in coding sequences. Therefore, we could create alleles of the tagged gene that confirmed causation of the dek phenotype by the Dsg insertion. The mutation, designated dek38-Dsg, is embryonic lethal, has a defective basal endosperm transfer (BETL) layer, and results in a smaller seed with highly underdeveloped endosperm. The maize dek38 gene encodes a TTI2 (Tel2-interacting protein 2) molecular cochaperone. In yeast and mammals, TTI2 associates with two other cochaperones, TEL2 (Telomere maintenance 2) and TTI1 (Tel2-interacting protein 1), to form the triple T complex that regulates DNA damage response. Therefore, we cloned the maize Tel2 and Tti1 homologs and showed that TEL2 can interact with both TTI1 and TTI2 in yeast two-hybrid assays. The three proteins regulate the cellular levels of phosphatidylinositol 3-kinase-related kinases (PIKKs) and localize to the cytoplasm and the nucleus, consistent with known subcellular locations of PIKKs. dek38-Dsg displays reduced pollen transmission, indicating TTI2's importance in male reproductive cell development.

Maize kernels do not contain enough of the essential sulphur-amino acid methionine (Met) to serve as a complete diet for animals, even though maize has the genetic capacity to store Met in kernels. Prior studies indicated that the availability of the sulphur (S)-amino acids may limit their incorporation into seed storage proteins. Serine acetyltransferase (SAT) is a key control point for S-assimilation leading to Cys and Met biosynthesis, and SAT overexpression is known to enhance S-assimilation without negative impact on plant growth. Therefore, we overexpressed Arabidopsis thaliana AtSAT1 in maize under control of the leaf bundle sheath cell-specific rbcS1 promoter to determine the impact on seed storage protein expression. The transgenic events exhibited up to 12-fold higher SAT activity without negative impact on growth. S-assimilation was increased in the leaves of SAT overexpressing plants, followed by higher levels of storage protein mRNA and storage proteins, particularly the 10-kDa δ-zein, during endosperm development. This zein is known to impact the level of Met stored in kernels. The elite event with the highest expression of AtSAT1 showed 1.40-fold increase in kernel Met. When fed to chickens, transgenic AtSAT1 kernels significantly increased growth rate compared with the parent maize line. The result demonstrates the efficacy of increasing maize nutritional value by SAT overexpression without apparent yield loss. Maternal overexpression of SAT in vegetative tissues was necessary for high-Met zein accumulation. Moreover, SAT overcomes the shortage of S-amino acids that limits the expression and accumulation of high-Met zeins during kernel development.